The present invention relates generally to turbocharged internal combustion engines, and, more specifically, to turbocharger systems having a wastegate control valve for controlling exhaust flow to a turbocharger.
A limiting factor in the performance of an internal combustion engine is the amount of combustion air that can be delivered to the intake manifold for combustion in the engine cylinders. Atmospheric pressure is often inadequate to supply the required amount of air for efficient operation of an engine.
It is known to use turbochargers in the intake air supply of internal combustion engines to increase the combustion air supplied to the combustion cylinders. Each turbocharger typically includes a turbine having a turbine wheel driven by exhaust gases from the engine, and one or more compressors having compressor wheels driven by the turbine through a common turbocharger shaft carrying both the turbine wheel and the compressor wheel. The compressor receives the fluid to be compressed, and supplies the compressed fluid to the combustion chambers. The fluid compressed by the compressor may be in the form of combustion air only, or may be a mixture of fuel and combustion air. Through the use of a turbocharger, the power available from an engine of given size can be increased significantly. Thus, a smaller, less expensive engine may be used for a given power requirement, and power loss due to, for example, changes in altitude, can be compensated for.
Under some conditions, a turbocharger can provide combustion air at too great of pressure for the intake manifold or combustion cylinders, leading to possible engine damage. Overspeed operation of a turbocharger can lead to damage to the turbocharger as well. It is known to use a wastegate control valve in the exhaust flow stream to the turbocharger. A branch line of the exhaust system bypasses the turbine wheel of the turbocharger. Operation of the wastegate valve can direct exhaust flow through the bypass line, thereby reducing the exhaust gas flow to the turbine wheel, reducing turbine wheel speed and thereby the boost or pressure of air supplied by the turbocharger compressor.
It is known to use both mechanical and electrical control systems for wastegate valve operation. U.S. Pat. No. 6,012,289 entitled xe2x80x9cApparatus and Method for Utilizing a Learned Wastegate Control Signal for Controlling Turbocharger Operationxe2x80x9d, assigned to the assignee of the present invention, discloses a method for controlling an engine turbocharger having a wastegate control valve. The turbocharger is controlled by an electronic controller, which is capable of delivering a wastegate control signal to the wastegate control valve.
Turbocharged internal combustion engines having wastegate control valves can experience additional difficulties in operation at high altitude, due to the reduced atmospheric pressure. The reduced atmospheric pressure can result in unfavorable pressure differences across the wastegate diaphragm. The wastegate may not be able to open under the given control system, or may open less than required, causing higher than acceptable turbine inlet pressures. Machines operated at both high and low altitude locations are not easily outfitted with control strategies that will take into consideration the effects of changing altitudes on the wastegate control valve operation.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one form thereof, the present invention provides an internal combustion engine with a combustion cylinder; an exhaust system in flow communication with the combustion cylinder, to receive exhaust gases from the combustion cylinder; a combustion air system connected in flow communication to the combustion cylinder, to supply air to the combustion cylinder for supporting combustion; and a turbocharger. The turbocharger includes a compressor having an inlet and an outlet, a turbine having an inlet connected to receive a flow of exhaust gases from the combustion cylinder, and a wastegate valve for controlling the flow of exhaust gases to the turbine. The wastegate valve includes a valve housing, and a valve diaphragm in the valve housing separating the valve housing into first and second valve compartments having a first valve compartment pressure and a second valve compartment pressure. One of the first and second valve compartment pressures is ambient pressure. A valve rod is connected to the valve diaphragm. A spring is operatively connected to exert a spring force against the valve rod, the spring having an installed spring length. An adjustable spring seat is adjustable in height, for varying the installed spring length of the spring in response to changes in the ambient pressure.
In another form thereof, the present invention provides a wastegate with a valve housing, a valve diaphragm in the valve housing separating the valve housing into first and second valve compartments having a first valve compartment pressure and a second valve compartment pressure. One of the first valve compartment pressure and the second valve compartment pressure is ambient pressure. A valve rod is connected to the valve diaphragm. A spring is operatively connected to exert a spring force against the valve rod, the spring having an installed spring length. An adjustable spring seat is adjustable in height, for varying the installed spring length of the spring in response to changes in the ambient pressure.
In yet another form thereof, the present invention provides a method for controlling operation of a wastegate valve, the method comprising steps of: providing a wastegate valve having a valve housing, a valve diaphragm separating the valve housing into first and second valve compartments, a valve rod connected to the valve diaphragm and extending through one of the compartments, and a spring operatively connected to exert a spring force against the valve rod, for urging the rod in a direction, the spring having an installed spring length; providing an adjustable spring seat for altering the spring force applied against the rod; detecting ambient pressure changes; and adjusting the spring seat in response to changes in ambient pressure.